2. Pod corn. It was discovered this season
that our homozygous stock of pod corn, as reported in a previous Letter,
carries an allele intermediate between ordinary Tu and tu
in its effects. We designate this tui. This raised the question of whether there are other
weak alleles of Tu among living
varieties. An examination of our collection of Latin American varieties
indicates that many of the varieties of Mexico, Guatemala, Colombia, Ecuador,
Peru and Bolivia may possess weak alleles of Tu. There is some genetic evidence for such a
conclusion in F1 hybrids of United States and Latin American
varieties with an inbred strain of intermediate tunicate. More than 100 such
crosses (originally made to test for minus modifiers of Tu) were grown in 1947. The ears in different crosses
varied from those in which the grains were completely covered with glumes to
those in which the glumes were so reduced that the ears had the aspect of
normal non‑tunicate ears. Plus and minus modifiers for tunicate are
undoubtedly responsible for part of this variation, but the major part is
probably due to weak alleles of Tu
possessed by many of the Latin American varieties.

The reak tunicate condition, like intermediate and
strong tunicate, is often associated with a flexible cob. In two different
crosses, one involving the Guarany maize of Paraguay and the other a variety
from Guatemala, flexibility of the cob was associated with the Su gene on the fourth chromosome. In one of these
crosses, the percentage of crossing over between Su and flexibility was 31 per cent, which is
approximately the same as previously reported between Su and Tu.
Apparently the flexibility of the cob of some varieties is due to a weak allele
of Tu.

An examiniation of prehistoric ears from Peru
indicates that all, or practically all, are similar to the weak tunicate
condition found in some modern Latin American varieties.

There are indications that Tu is a mutable locus. The gene tui apparently arose as a mutation in our Tu stock. More recently we have found a chimera in a Tutu stock in which part of the seeds were covered with
glumes and part were naked. Covered seeds, when grown, gave rise to TuTu,
Tutu, and tutu individuals; naked seeds produced only Tutu and tutu plants. Numbers are too small to prove the case but are suggestive.

The case for pod corn as the ancestral condition of
cultivated maize is now perhaps as complete as it can be on the basis of
circumstantial evidence. These are the salient facts:

1.
Ears resembling pod corn are represonted on prehistoric pottery.

2.
One prehistoric ear of pod corn is known.

3. The majority of prehistoric Peruvian ears appear
to be a weak form of pod corn.

4.
There are several historical references to pod corn in South America.

5.
Many living varieties, especially those of South America, possess a weak allele
of Tu.

6.
The tu gene is mutable.

7.
Pod corn possesses the principal characteristic which the comparative
morphologist would expect to find in a wild maize ancestor.